Hi Clint, There seems to have been very little information available from Halcyon on either the OFS or PFS off air references. All I've seen is the OFS alignment document that Stephen is already sending to you. There were two versions of the OFS1, the later version had similar proportions to a Quartzlock 2A whilst the earlier was in a taller case and not so wide. That board in the alignment notes seems to match reasonably closely to a couple of photos I have of the earlier circuit board. I'll send you copies of those photos for reference as they might help you pinpoint any changes if they match your unit, but I've got no information on the later board so not sure how similar that might be. The off air section of the PFS1 was significantly different to the earlier OFS1 at least. Nigel, GM8PZR I have been given a Halcyon Electronics OFS1 standard which seems to work, it's a version that has 198KHz and 162KHz selector on the fron and after areasonable period of time it displays 'lock' and gives a nicely stable 1,10 and 10 MHz output on the front panel BNCs, (I know, it should be 1,5 and 10MHz out, read on) Does anyone know of a PDF manual? This version has two KHz crystals insideit and I'd like to see how/if it's been modified so a manual with a schematic would be even more useful. Clint